This invention relates to apparatus for friction or spin welding thermal plastic parts to a thermal plastic work piece.
Various techniques have been used to fuse thermal plastic fasteners or parts and work pieces together. The techniques generally involve frictionally heating the interface between the plastic part and the work piece by applying contact pressure while at the same time rotating the members relative to one another. When the interface of the two members has achieved molten state, the rotation is stopped while the contact pressure is maintained for a time sufficient to allow the interface to solidify. The length of time required to achieve a molten interface depends upon a variety of factors including plastic part material, work piece material, the size and configuration of the interface, the amount of contact pressure, the speed of rotation, the thermal dissipation characteristics of the connection, the dynamic friction characteristics of the interface, and other factors. After the molten state at the interface is achieved, it is necessary to continue to apply contact pressure until the interface returns to the solid state and the time required in this step varies with the materials involved.
A friction welded fastener system wherein a fastener or plastic part is friction welded to a work piece is disclosed in U.S. Pat. No. 4,477,307. In the type of friction welding apparatus disclosed in that patent a standard pneumatic tool or driver is equipped with a nose piece and driver assembly to hold the plastic part in place during the friction welding operation. The plastic part is held in place by a "press fit" between the plastic part body and the driver assembly. It is necessary that an operator manually load the plastic part onto the driver assembly and then initiate the friction welding operation. Such apparatus cannot apply fasteners or plastic parts to a work piece automatically. Ideally, a friction welding operation should be automated to reduce labor costs and improve production efficiency. To do so it is necessary to orient and feed the plastic parts to the friction welding apparatus, have the plastic parts picked up positively by the friction welding apparatus, sense the presence or absence of the plastic part on the friction welding apparatus, and if the plastic part is present, proceed with the friction welding operation to join the plastic part to the work piece.
By the present invention friction welding apparatus is provided that will automatically place the plastic part on the apparatus, sense whether or not a plastic part is actually present on the apparatus and the plastic part is gripped through the use of vacuum pressure to be maintained on the apparatus during the friction welding operation.